Question

Water is pumped from a lake to a storage tank 20m above at a rateof
70 L/s while consuming 20.4kW of electric power. Disregardingany
frictional losses in the pipes and any changes in kineticenergy,
determine a) the overall efficiency of the pump-motor unitand b)
the pressure difference between the inlet and exit of
thepump.

- I figured I'd be using the equation ηpump =(ΔEmech,
fluid)/(Wshaft, in) do determine efficiency. I justcan't seem to
find a good explanation on using height differenceand volumetric
flow rate to determine (ΔEmech, fluid) in mybook. Does anyone have
an idea how to do this?